Fluid flow meter

ABSTRACT

A mass fluid flow sensor for determining the amount of fluid inducted into an internal combustion engine, for example, is disclosed. The mass fluid flow sensor includes an external intake fluid temperature element which improves the accuracy of the mass fluid reading. An external cold wire element is further provided which improves response time. The mass fluid flow sensor has an improved aerodynamic design which provides a lower system pressure drop. Moreover, the sensor is smaller and lighter and has fewer parts, thus providing better manufacturability. A molded one-piece isolated jet nozzle having a hot element disposed therein is included in the fluid sampling portion. Consequently, an improved lower internal flow passage pressure drop is achieved. Additionally, an improved signal to noise ratio, as well as a larger dynamic range is an advantageous consequence of the present invention. The present invention further provides improved electromagnetic interference performance.

TECHNICAL FIELD

The present invention relates to devices and methods for measuring fluidflow in a duct.

BACKGROUND OF THE INVENTION

Internal combustion engines today include electronic controls to provideoptimal engine operation. Typically, the electronic control systemsinclude a primary control unit for processing control algorithms and avariety of sensors for providing control signals to the primary controlunit. One critically important sensor for achieving optimal enginecontrol is a mass fluid flow sensor for measuring air intake into theinternal combustion engine.

It is critical that the mass fluid flow measurement is accurate in orderto provide optimal engine operation. One significant problem affectingthe mass fluid flow measurement, is reverse flow or back flow in thedirection opposite of fluid intake. Typically, mass fluid flow sensorsdetect the flow of air in both the forward and reverse directionsrelative to air intake, therefore reverse flow causes an inaccurate massfluid flow reading.

Prior art mass fluid/air flow devices have attempted to address thisproblem by providing mass air flow sensor configured as disclosed inU.S. Pat. No. 5,556,340 issued to Clowater et al. In Clowater, a massair flow sensor having a U-shaped air passage and a longitudinallyconverging elliptical inlet configuration is disclosed, and herebyincorporated by reference. This configuration increased measurementefficiency and reduced the effect of back flow on the measurement of airflow into the internal combustion engine. Further, such a configurationproduces advantageously low signal to noise ratio, as well as highvelocity across the mass fluid flow sensor element.

While prior art mass fluid flow sensors, such as the one disclosed inClowater, significantly improved the accuracy of the mass fluid flowmeasurement. Improvements are still needed to address other problems.

For example, it would be advantageous to provide a mass fluid/air flowsensor having improved response time, a more aerodynamic design, havinga lower system pressure drop, an improved internal flow passage pressuredrop, in improved signal to noise ratio, an improved electromagneticinterference performance, and fewer parts to achieve less manufacturingcomplexity.

BRIEF SUMMARY OF THE INVENTION

In an embodiment of the present invention, a mass fluid flow sensor isprovided for determining the amount of air inducted into an internalcombustion engine, in accordance with the present invention. The massfluid flow sensor of the present invention includes an external intakeair temperature element which improves the accuracy of the mass airreading. An external cold wire element is further provided whichimproves response time. The mass fluid flow sensor of the presentinvention has an improved aerodynamic design which provides a lowersystem pressure drop. Moreover, the sensor is smaller and lighter andhas fewer parts, thus providing a better manufacturability. For example,a molded one-piece isolated jet nozzle having a hot element disposedtherein is provided in a flow passage of the sampling portion of thehousing. Consequently, an improved lower internal flow passage pressuredrop is achieved. Additionally, an improved signal to noise ratio, aswell as a larger dynamic range is an advantageous consequence of thepresent invention. The present invention further provides improvedelectromagnetic interference performance.

In an embodiment of the present invention, a mass fluid flow sensorhaving a circular opening or inlet of the nozzle is provided.

In another embodiment of the present invention, control electronics arelocated in a longitudinally extending section of the mass fluid flowsensor housing above the sampling portion. Thus, the present inventionprovides an integrated circuit cavity and sampling portion in onepackage.

In another aspect of the present invention, a U-shaped flow passage isprovided for capturing a sample of the intake air.

In yet another embodiment of the present invention, an outlet of theU-shaped flow passage is provided to allow the fluid to exit and flowout of the bottom of the flow passage, as well as, the sides of thehousing.

In yet another embodiment of the present invention, a measuring elementis located within the flow passage at the exit or outlet of the jetnozzle, in accordance with the present invention.

In yet another aspect of the present invention, the measuring element iscentered at the exit of the converging nozzle.

In still another embodiment of the present invention, the controlelectronics are located adjacent the flow passage within the circuitcavity.

Further objects, features and advantages of the invention will becomeapparent from consideration of the following description and theappended claims when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a mass fluid flow sensor in accordancewith the present invention;

FIG. 2 is a perspective view of a mass fluid flow housing in accordancewith the present invention;

FIG. 3 is a perspective view of a mass fluid flow housing cover, inaccordance with the present invention;

FIG. 4a is an inside perspective view of a mass fluid flow housingcover, in accordance with the present invention;

FIG. 4b is an outside perspective view of the housing with the housingcover installed thereon, in accordance with the present invention;

FIG. 4c is a perspective view of the housing with the housing coverinstalled thereon, in accordance with the present invention;

FIG. 5 is a perspective inside view of an electronics cover for a massfluid flow sensor, in accordance with the present invention;

FIG. 6 is an outside view of an electronics cover of a mass fluid flowsensor, in accordance with the present invention;

FIG. 7a is a fully assembled perspective view of a mass fluid flowsensor in accordance with the present invention;

FIG. 7b is a cross-sectional view through the mass fluid flow sensor asindicated in FIG. 7a in accordance with the present invention; and

FIG. 8 is cross-sectional view through an automotive fluid intakemanifold and further illustrated in exemplary location of the mass fluidflow sensor, in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1 and 2, exploded and perspective views of a massfluid flow sensor 10 for calculating the amount of fluid flowing in aduct is illustrated, in accordance with the present invention. Oneapplication or use for sensor 10 is for measuring the amount of airinducted into an internal combustion engine (not shown). However, thepresent invention contemplates other uses and application for sensor 10.For example, sensor 10 may be used to calculate the amount of fluid(other than air) flowing through a duct (other than an air intake ductof an internal combustion engine). Mass fluid flow sensor 10 includes ahousing 12, housing cover 14, a secondary housing cover 16, anelectronics cover 18, and a gasket 20.

Housing 12 includes an integral connector 30 having connector terminals(not shown) that are in electrical communication with engine operationcontrol electronics external to mass fluid flow sensor 10 and inelectrical communication with a circuit module 32 disposed within acentral housing portion 34. Adjacent to central housing portion 34,housing 12 further provides an integrally attached fluid samplingportion 36. Fluid sampling portion 36 includes an inlet 38 that opensinto a nozzle 39. Nozzle 39 communicates with a substantially U-shapedflow passage 40. U-shaped flow passage 40 terminates at an outlet 42.

Nozzle 39 has, generally, a jet nozzle configuration or shape. As willbe further illustrated and described, nozzle 39 is defined by agenerally circular opening or inlet 38 that meets longitudinallyconverging elliptical side surfaces (as shown in FIG. 7b). Thelongitudinally converging elliptical side surfaces of the nozzle createa relatively high pressure at an exit 41 of nozzle 39. Further, the jetnozzle configuration of nozzle 39 creates a critical area 43 located atexit 41 having a uniform fluid flow velocity across the critical area.This critical area created by the nozzle provides enhanced fluid flowdetection and measurement as will be described hereinafter. To furtherenhance the flow of fluid through passage 40 a wedge deflector 45 ispositioned on an end of housing 12 upstream of outlet 42. Wedgedeflector 45 has a surface that is tilted to create an advantageouslylow pressure area adjacent outlet 42. If the angle of the surface ofdeflector 45 (indicated by the letter a in FIG. 7b) is too small withrespect to the direction of fluid flow an insufficient pressure drop iscreated at outlet 42. Conversely, if the angle of the surface ofdeflector 45 is too large with respect to the direction of fluid flow aninsufficient pressure drop is created at outlet 42.

As illustrated in FIG. 2, a plurality of resistive elements areoperatively disposed and supported by housing 12 and are in electricalcommunication with circuit module 32 via electrical conductors, such asintegrally molded leads or terminals. The resistive elements include ahot wire element 44, a cold wire element 46 and an internal fluidtemperature (IAT) element 48. Generally, these elements changeresistance as a function of temperature.

Circuit module 32 senses a fluid, such as, air flowing through passage40 by monitoring the power dissipated by the elements. Circuit module 32may be a single integrated circuit chip or a substrate having discrete,as well as, integrated circuits mounted thereon. The sensed resistancechange in the elements is converted to an output signal that is receivedby the electronic engine control system (not shown). Typically, theelectronic engine control system regulates the quantity of fuel injectedinto the engine by controlling the air to fuel ratio.

The IAT or element 48 is generally a thermister or similar device.Element 48 is located on housing 12 to insure an accurate reading of thetemperature of the air charge during the induction cycle of the internalcombustion engine. As shown in FIG. 2, element 48 is located,preferably, external of passage 40 to minimize the fluid heating effectscaused by the heat dissipation from hot element 44.

In a preferred embodiment of the present invention, a fluid flow sensor10 is provided having elements 44 and 46 made of platinum wire woundresistors. Generally, these elements have a positive temperaturecoefficient. Thus, any resistive changes in the elements will correspondwith a temperature change in the same direction. That is, if thetemperature increases, the resistance will increase, and if thetemperature decreases, the resistance will decrease. Preferably, hotelement 44 is located at exit 41 of nozzle 39 and within the criticalarea 43. The location of the hot element within the critical areainsures that fluid, having the same velocity, flows over the hot elementcausing heat to dissipate evenly across the entire surface of theelement. Thus, the present invention provides enhanced fluid flowdetection.

In an embodiment of the present invention, hot element 44 may forexample have a resistance of 20 Ohms at 70° F. Thus, if the temperatureincreases by 10° F. the resistance of the hot wire will increase byapproximately 0.025 Ohms. The hot element 44 is used primarily fordetecting the velocity of the fluid flowing through passage 40 fromwhich the mass of fluid flowing through passage 40 may be derived.

The cold wire element 46, may for example have a nominal resistance of500 Ohms at 70° F. If the temperature of the cold wire is increase by10° F. the resistance of cold wire will increase by approximately 0.5Ohms. The primary purpose of the cold wire element 46 is to providetemperature correction.

In operation hot wire element 44 is held at approximately 200° F. abovethe ambient temperature. This is accomplished by placing the hot wireelement in a voltage divider circuit. With reference to FIG. 3, anexemplary voltage divider circuit 500 for fixing hot wire element 44 ata desired constant resistance and temperature is illustrated, inaccordance with the present invention. In an embodiment of the presentinvention circuit 500 is disposed in integrated circuit 32, along withother control circuitry. Exemplary circuit 500 includes two voltagedivider networks 502 and 504 in communication with an operationalamplifier 506. Voltage divider network 502 generally has two 500 Ohmresistors 508 and 510 which form a 50% voltage divider network and forceplus pin 512 of op-amp 506 to half the output voltage on line 518. Theother voltage divider network 504 includes generally a 25 Ohm resistor514 in series with the hot wire element 44. The minus pin 516 of op-amp506 is connected between resistor 514 and hot wire element 44. Thus theratio of this network starts with a ratio of 20 Ohms to 45 Ohms, sominus pin 516 is forced to 20/45^(th) of the output voltage. Forexample, the op-amps output voltage on output line 518 will increase ifthe voltage on plus pin 512 is greater than the voltage on the minus pin516. Likewise, the output voltage on line 518 will decrease if thevoltage on plus pin 512 is less than the voltage on minus pin 516.Accordingly, the op-amp's output voltage on line 518 will increase ordecrease by a voltage amount necessary to force the voltage on plus pin512 to equal the voltage on minus pin 516.

Since resistor network 502 provides a greater voltage on plus pin 512that is 50% of the output voltage as compared to 44% on minus pin 516,the op-amps output voltage will increase on line 518. As the voltageincreases, the power dissipated by the hot wire element 44 causes anincrease in resistance of the hot element. It takes approximately onequarter watt of power in still air to increase the temperature of hotelement 44 by 200° F. A 200° F. increase in temperature raises hot wireelement 44's resistance by 5 Ohms. The ratio of the hot wire resistanceat the increased temperature to the total resistance in resistor network504 forms a 50% voltage divider network. Thus, the plus and minus pins512 and 516 of op-amp 506 are at the same voltage since both networks502 and 504 form 50% voltage divider networks. Thus the temperature ofhot wire element 44 is forced to approximately 270° F.

The circuit 500 provides an output on line 518 to an electronic enginecontrol module (not shown) which determines the proper air fuel ratiofor optimal engine operation, as well known in the art. Since it takes aquarter watt as disclosed above for voltages on plus and minus pins 512and 516 to be equal, the voltage across the hot wire element 44 andresistor 514 can be calculated using the equation:Power=(voltage)²/resistance and then solving for voltage (V):V=(power×resistance)^(1/2) or (0.25×25)^(1/2). Since the voltage acrossresistors in series add the nominal output of the circuit is 5 volts forno air flow. Obviously, more circuitry would be used to level shift andamplify the output of the circuit 500.

As air flows over hot wire element 44, power in the form of heat istransferred from the hot wire element to the air. Heat removed from thehot wire element 44 causes the resistance of element 44 to decrease.Decreasing resistance causes the voltage applied to the minus pin 516 todecrease. Accordingly, the output voltage on line 518 would increasecausing more power to be dissipated by the hot wire element 44. Thus,the increase in power dissipated by the hot wire element causes thetemperature of element 44 to increase and return to 270°. When thistemperature is reached, the voltage on pins 512 and 516 of op-amp 506will be at equilibrium.

Accordingly, since the circuit regulates the resistance of hot wireelement 44 the output of the circuit on line 518 is proportional to thesquare root of the power removed from the hot wire times two minus 5volts, for example. Nominal power dissipated by the hot wire element 44is one-quarter of a watt which is the amount of power needed to keep thehot wire element 44 at 270° F. Any heat removed from the hot wire isreplaced by applying more power to element 44. Resistance of the hotwire is regulated to 25 Ohm thus resistance is considered to beconstant. Power removed equals the power applied minus the amount neededto maintain the hot wire at 270° F. Solving the power formula forvoltage: v=(power×resistance)1/2, any increase in power applied to thehot wire element 44 is also applied to the 25 Ohm resistor. Therefore,the voltage necessary to compensate for power removed from element 44 isdoubled.

For proper operation of sensor 10, the temperature of hot wire element44 needs to be maintained at 200° F. above ambient temperature. If theambient temperature is constant there is no need for temperaturecorrection. That is, a constant difference in temperature guarantees thesame amount of power will be removed from the hot wire element 44 for agiven air flow. However, when an fluid flow sensor is placed in anautomobile (as shown in FIG. 8), ambient air temperature is notconstant. Typically, sensor 10 will be exposed to temperatures belowfreezing and above boiling. Thus, air flow temperatures lower thanexpected will cause a larger than desired output voltage andtemperatures higher than expected will cause a lower than desired outputvoltage.

The present invention provides temperature correction to compensate forthe variable ambient temperature environment present in an automobile.Temperature correction is achieved through the use of the cold wireelement 46. The cold wire element 46 is placed in resistor network 502in place of resistor 510, as illustrated in FIG. 3. Circuit 500 usescold wire element 46 for temperature compensation. Element 46 issupported by housing 12 and is placed in the air stream outside of flowpassage 40. Placing cold wire element 46 in the air stream allows thecircuit to quickly respond to changes in the ambient air temperature.The temperature of cold wire element 46 will follow the temperaturechanges of the incoming air. Since the resistance of the cold wireelement (500 Ohms) is relatively large compared to the voltage dropacross the element, the power dissipated is very small. For example, at70° F. the resistance of element 46 is 500 Ohms with a voltage drop of2.5 volts. Moreover, the power dissipated by element 46 is 0.0125 wattswhich results in a temperature increase of about 10° F.

Accordingly, the resistance of the cold wire element 46 would increaseby 5 Ohms and resistor network 502 resistance ratio would change. Forexample, the voltage applied to plus pins 512 would equal 505/1005 or50.25% of the output voltage on line 518. In turn resistor network 504will also have to form a ratio equal to 50.25% of the output voltage.Thus, to form the same ratio, the hot wire resistance would need to bemaintained at 25.25 Ohm to develop the same resistance ratio of 50.25%thus the hot wire element 44 will be maintained at 200° above the coldwire element 46 or 280° F. if the ambient temperature is 70° F. Coldwire element 46 is 100 above the ambient temperature of 70° F. Thus, thetemperature difference that is necessary for handling environmentalextremes is maintained. The nominal output of this circuit is still fivevolts. It takes ¼ watt of power to raise the temperature of the hot wireelement by 200° degrees Fahrenheit. Solving the power equation forcurrent (i), i=(power/resistance)^(1/2). Thus, current in the hot wirenetwork equals 0.099503 amps ((0.25/25)^(1/2)). The output voltage isthen (0.099503×50.25), which is approximately five volts. The circuit inFIG. 3 can dynamically adjust to ambient air temperature changes becausethe change in the cold wire network is directly proportional to theproperties of the hot wire network.

The values for resistance and changes in resistance are solely forexplanatory purposes and other values certainly may be used.

Referring now to FIGS. 4a and 4 b, a perspective view of housing cover14 is further illustrated, in accordance with the present invention.FIG. 4a is an inside view of housing cover 14 and FIG. 4b is an outsideview of housing cover 14. Housing cover 14 is fixedly joined to housing12 (as shown in FIG. 4c) along a protruding ridge 60 and 62. Ridge 60protrudes from an inside surface 64 of housing cover 14 and matinglyseals with channel 50 disposed on an inside surface 52 of housing 12.Ridge 62, protruding from an inside surface 64 of housing cover 14,matingly seals with channel 54 disposed within surface 52 and around theperimeter of flow passage 40, thus creating an enclosed and sealed flowpassage 40. Housing cover 14 further includes a window aperture 66 forproviding access, during manufacture, to integrated circuit 32 (as shownin FIG. 4c). For example, window aperture 66 provides access tointegrated circuit 32 during the calibration step in the manufacturingprocess. Further, as shown in FIG. 4c, integrated circuit 32 is wirebonded using wire bonds to various terminal and/or bonding pads disposedon housing 12.

As shown in FIG. 4b a channel 68 is provided around a perimeter ofwindow 66 to matingly seal the secondary housing cover 16 to housingcover 14. Further, a side opening 70 allows air exiting flow passage 40to flow out of both side surfaces 72 and of cover 14. A ramped portion75 is included in surface 72 to funnel and direct air passing over thesurface toward cold wire element 46

A perspective inside view of secondary housing cover 16 is illustratedin FIG. 5. Cover 16 includes a perimeter ridge protrusion 80 whichmatingly seals with housing cover 14 along the perimeter of window 66and within channel 68. Secondary housing cover 16 is substantially flatand maybe constructed of a heat conductive material, such as a metal fordissipating heat generated by integrated circuit 32. As shown in FIG. 1,secondary housing cover 16 has a generally planar outside surface 84.After cover 16 is positioned on housing cover 14, both the cover 14 andthe secondary housing cover 16 create a longitudinally extending andgenerally planar surface to insure minimal disturbance of the airflowing around sensor 10.

A perspective inside view of electronics cover 18 is illustrated in FIG.6. In an embodiment of the present invention integrated circuit 32 isbonded to cover 18 and the resulting circuit and cover assembly isloaded into and matingly seals against housing 12. Cover 18 has aprotruding ridge 83 rising from a surface 85 of cover 18. Protrudingridge 83 sealingly mates with a corresponding channel (not shown)disposed on housing 12 to created a weather resistant sensor housing.Preferably, cover 18 functions as a heat sink to draw heat emanatingfrom circuit module 32. In an embodiment of the present invention, heatsink 18 is made from a metallic material or other material havingsimilar thermal conductive properties.

A perspective view of a fully assembled mass fluid flow sensor 10 isillustrated in FIG. 7a, in accordance with the present invention. Aflange 90 is integrally formed in housing 12 and includes a plurality ofmounting apertures 92 and 94. Mounting apertures 92 and 94 receivefasteners (not shown) such as screws for securing sensor 10 to amounting surface. Further, flange 90 has a mating surface 96 formatingly engaging an engine air intake duct 304 (shown in FIG. 8) aswill be described below. Gasket 20 which is configured to engage aflange ledge or shelf 98 is positioned between the engine intake ductand flange 90 to provide an air tight seal between mass fluid flowsensor 10 and air intake duct 304.

As illustrated in FIG. 7a, air flows into inlet 38 of mass fluid flowsensor 10 in a direction, as indicated by arrow i, and out of outlet 42in a direction, as indicated by arrows O. Inlet 38 is generally circularand as illustrated in FIG. 7b has a generally elliptical cross-section.

With specific reference to FIG. 7b, elliptical surfaces 200 which definethe perimeter of inlet 38 and nozzle 39. Moreover, as shown, ellipticalsurfaces 200 converge along a longitudinal axis 202, creating an inletand nozzle having a longitudinally converging elliptical surface. Thisinlet and nozzle configuration is known as a jet nozzle. Further, it isknown that this jet nozzle configuration creates a critical area, at theexit of the nozzle, having a uniform fluid flow velocity. As statedabove the present invention has improved accuracy as compared to theprior art because, for example, the hot element 44 is located in thecritical are and therefore is evenly cooled by incoming fluid.

Referring now to FIG. 8, an exemplary automotive environment in which amass fluid flow sensor may be operatively disposed is illustrated, inaccordance with the present invention. Typically, an automotive vehiclehas an air intake manifold 300 for supplying fresh air to the vehicle'sengine (not shown). Generally, air intake manifold 300 includes a filter302 for filtering the intake air and extract contaminants from the airdrawn into manifold 300.

Air intake manifold 300 is typically attached to an air duct 304 forcommunicating the clean air to the vehicle's engine. As illustrated,mass fluid flow sensor 10 is positioned and fixedly secured to air duct304 through an aperture 306 in air duct 304. Outside air is drawn intointake manifold 300 in a direction indicated by arrow A and flowsthrough manifold 300 as indicated by arrows A′ and A″. When the intakeair reaches air duct 304, a portion of the intake air flows into themass air flow sensor, as indicated by arrow i, and then out of the massfluid flow sensor as indicated by arrow o. All of the intake aireventually exits air duct 304 and enters the vehicle's engine, asindicated by arrow e. Electrical control signals containing informationregarding the amount of air flowing through the air duct 304, derivedfrom measurements and processing carried out on integrated circuit 32,is communicated to the vehicle's electronic control systems through aconnector 308 and wire harness 310.

The present invention contemplates an assembly and/or manufacturingmethod or process for constructing mass fluid flow sensor 10. In aninitial step the resistive elements are electrically connected to thehousing using solder or other like material. At a next step, theelectronics cover 18 and integrated circuit 32 assembly is mounted tothe housing 12, using an adhesive or similar material. At a next step,the housing cover 14 is mated to housing 12 and bonded thereto using anadhesive or similar material. At a next step, the assembly is placed inan oven or other environment suitable for curing the adhesive. At a nextstep, the integrated circuit 32 is wire bonded to terminals and/orbonding pads on housing 12. At a next step, the integrated circuit 32 iscalibrated and/or adjusted and/or resistors disposed within circuit 32are trimmed. At a next step, the secondary housing cover 16 is mated tohousing 12 and bonded thereto using an adhesive or similar material. Ata final step, sensor 10 is tested to insure proper function at differentoperating states and environmental conditions.

The foregoing discussion discloses and describes a preferred embodimentof the invention. One skilled in the art will readily recognize fromsuch discussion, and from the accompanying drawings and claims, thatchanges and modifications can be made to the invention without departingfrom the true spirit and fair scope of the invention as defined in thefollowing claims.

What is claimed is:
 1. A device for detecting a mass of a flowing fluid,the device comprising: a housing positionable within a fluid carryingduct having a fluid sampling portion and a circuit cavity portion,wherein the fluid sampling portion includes a flow passage; a nozzle influid communication with the flow passage, wherein the nozzle has aplurality of longitudinally converging elliptical side surfaces thatterminate at a nozzle exit; a first electrical element disposed in theflow passage at the nozzle exit; a second electrical element supportedby the housing external of the flow passage; and a circuit module incommunication with the first and second electrical elements and disposedin the circuit cavity portion for detecting a change in an electricalproperties of the first and second electrical elements, wherein thedetected change in the electrical properties are used to determine themass of the flowing fluid.
 2. The device of claim 1 wherein the secondelectrical element is used for temperature correction.
 3. The device ofclaim 1 further comprising, a cover attachable to the housing forenclosing the fluid sampling portion and the circuit cavity portion. 4.The device of claim 1 further comprising, a heat sink in thermalcommunication with the circuit module.
 5. The device of claim 1 furthercomprising, a wedge deflector integrally attached to the housing forcreating a low pressure area at an outlet of the flow passage.
 6. Thedevice of claim 1 further comprising, a third electrical elementdisposed on the housing external of the flow passage.
 7. The device ofclaim 6 wherein the third electrical element is used for determining afluid temperature at the housing.
 8. The device of claim 6 wherein thethird electrical element is a thermister.